I have come to the conclusion that I must use the IAP function stored in the ROM.

How to call this, I am unsure.

The example given in the datasheet passes it two arguments. The EEFC ID (0 or 1) and the contents to write to the EEFC_FCR register.However, the description of the function specifies it only takes one argument.

In any case, I am unable to call it successfully. The Arduino simply hangs.